High temperature oxidation of Ni₂AlTi

Abstract

The isothermal oxidation process in bulk and powdered Ni₂AlTi (L2₁ structure) has been studied in the temperature range of 600 to 1200° C in air by means of X-ray diffraction and scanning electron microscopy. At 900 and 1200° C, the transient oxides, NiO and TiO₂ were formed in the initial stage on the outer surface. Subsequent oxidation was dominated by outward diffusion of aluminium, resulting in the formation of a Ni₃Ti layer beneath an internal precipitation layer containing Al₂O₃-NiAl₂O₄ aggregates, NiTiO₃ and Ni₃Ti. Formation of NiTiO₃ and NiAl₂O₄ at the expense of NiO, TiO₂ and Al₂O₃ indicated the reaction among constituent oxides also occurred in the late stage of oxidation at 900 and 1200° C. Only NiO and TiO₂ were identified in specimens oxidized at 600° C up to 24h. The oxidation rate of Ni₂AlTi is of the same order of magnitude as the dilute γ-NiAl alloy at 1200° C.